The above error occured when i ran sudo apt-get update on Ubuntu 14.04. After fetching the required updates it showed me an error at the bottom - W: GPG error: http://ppa.launchpad.net trusty InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY FE1FFCE65CB95493

Obviously , The solution is , we need to download keys from Ubuntu key server.. Now, see how to do that..

All You have to do to solve this problem is.. open the terminal and run the following command..

Friends , Don't forget to replace the FE1FFCE65CB95493 with the one included in your error message

However , i got timed out error, first time, when i ran this (gpg --keyserver subkeys.pgp.net --recv FE1FFCE65CB95493) .. but when i ran it second time ,it just works fine for me.. Hope it will be usefull.. Share it with your friends..